1. Field of the Invention
The present invention relates generally to the field of wire clips and, more particularly, to a capacitive pickup clip for detecting secondary voltage signals in an electronic ignition system.
2. Description of the Prior Art
Capacitive probes or pickup clips are well known in the field of automotive ignition system testing. Pickup clips respond to voltage changes in their immediate vicinity and are therefore useful in capacitively picking up the ignition pulses of an ignition system of an externally ignited internal combustion engine.
Capacitive pickup clips are most commonly used to detect voltage levels at a secondary ignition cable of ignition systems, including remote coil and distributorless ignition systems. The clips are connected directly over a current-carrying wire, thus making it unnecessary to disconnect wires or like ignition system components to measure the voltage at the wire.
As a voltage occurs in a wire, such as a secondary wire or cable of an ignition system, an electrostatic field is generated around the wire. By placing a capacitive pickup clip around the wire, the electrostatic field will be capacitively coupled to a plate or a washer within the clip causing a small voltage to be charge coupled thereto. The charge coupled voltage capacitively detected by the pickup clip is proportional to the voltage at the secondary wire. A wire connection coupled to the pickup clip ultimately communicates the detected voltage signals to an electronic unit, such as an engine analyzer or like waveform analyzing device.
Pickup clips are adapted with some means to effect hooking onto wires. One prior art capacitive pickup clip, manufactured by Bosch, Inc., includes spaced-apart, partially deflectable jaws formed integrally with an associated cap. The jaws have arcuate recesses on the inner facing surfaces thereof and are sized for engagement around a wire of fixed diameter. The Bosch clip is available with differently-sized, threadedly-engageable removable caps to effect use of the clip with wires of various sizes. The Bosch clip suffers the disadvantage of requiring a user to change caps when coupling to a larger or a smaller size wire.
Another type of prior art clip, manufactured by Snap-on, Inc., is provided with arcuate jaws joined at the wire receiving end thereof but separable when urged against a wire. Once the wire is engaged, the arcuate jaws enclose at least a portion of the received wire. The jaws are deflectable outwardly to accommodate wires of various sizes. Because the jaws are separable only at the receiving end, large size wires are not easily accommodated between the facing arcuate surfaces on the jaws. Also, clipping to an oversized wire could permanently deform the jaws, so that they would not firmly grip smaller wires. A poorly grasped wire may lead to inaccuracies in the detected voltage levels and may also result in the clip becoming disengaged from the wire under the weight of the clip pulling on the wire.
It would be a significant advancement in the art to be able to provide a capacitive pickup clip that can be used with a large range of differently-sized wires and which requires no interchangeable parts to achieve this end.
Conventional clips also suffer the disadvantage of two-handed wire-to-clip installation. The one hand of a user is generally required to hold the wire in a fixed position while the other hand is used to push the clip onto the wire, wedging the wire between the jaws. It would be an improvement in the art, therefore, to be able to provide a clip that permits clip-to-wire engagement with only one hand.